A dosimetric analysis of the aeroformTM tissue expander in radiation therapy
Purpose: The aim of this study is to evaluate the effects of the metallic reservoir and the use of gas within the Aeroform™ tissue expander with respect to the radiation dose distribution.
Methods: Dosimetric effects of using a metallic reservoir within a breast tissue expander during external beam radiotherapy were investigated. To view the internal components of the reservoir, it was removed from the tissue expander and imaged on a Varian AS500 electronic portal imager. To calculate the relative density of each component within the reservoir, an ionization chamber within solid water was used to measure the dose and compared to a simulation within the Pinnacle treatment planning system (TPS). To examine the relative dose profile along the length of the reservoir, the reservoir was exposed on EBT3 film and analyzed using SNC Patient™. In-vivo Dosimetry was performed using a RANDO® Woman phantom. Thermo-luminescent dosimeters were placed within the wax bolus enveloping the tissue expander.
Results: Imaging the reservoir on the electronic portal imager revealed it consists of 3 distinct components. The densities assigned in the TPS, which resulted in calculated doses which matched the measured doses were; Section 1 = 0 g/cm3, Section 2 = 2.8 g/cm3 and Section 3 = 0.7 g/cm3. Relative dose reductions were observed due to the metallic case; Section 1 = 20%, Section 2 = 40% and Section 3 = 30%. Entrance doses ranged from 2.39 - 2.53 Gy for both the medial and lateral beams. Exit doses ranging from 1.10 - 1.71 Gy were observed in both beams. There was a significant difference in measured and calculated doses at exit locations in the beam.
Conclusion: Dosimetric effects due to the metallic reservoir within the Aeroform breast tissue expander have been demonstrated and have been observed to be significant. To increase the dosimetric accuracy when contouring, individual components of the reservoir should be distinguished. Our in-vivo experiment showed that dose homogeneity was difficult due to the metallic reservoir and we recommend stringent patient dose monitoring when using this expander during radiotherapy.
Cite this article as: Tran T, Ding W, Subramanian B, Melven L, Chao M, Farrow H, Baker C. A dosimetric analysis of the aeroformTM tissue expander in radiation therapy. Int J Cancer Ther Oncol 2014; 2(3):020316. DOI: 10.14319/ijcto.0203.16
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International Journal of Cancer Therapy and Oncology (ISSN 2330-4049)
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